This invention relates generally to screenless completions for oil or gas wells. More particularly, the invention relates to designing screenless completions for oil or gas wells, which includes determining which wells are suitable for screenless completion and associating a particular predefined screenless completion design with a particular well and with wells of similar characteristic.
One stage in creating an oil or gas well is to complete the drilled borehole in a manner which hopefully enhances the production of oil or gas from the well. There are many different completion techniques; however, in general, completion preferably occurs so that the well will produce desired hydrocarbons and not undesired materials (e.g., formation solids) from one or more hydrocarbon-bearing formations intersected by the well bore. In some wells, mechanical equipment referred to as screens or gravel packs are lowered during completion into the well bore adjacent a formation from which production is to occur. Such equipment allows gas and liquid to flow through the screen or gravel pack structure during production, but it blocks formation solids which have larger diameters than the flow paths through the screen or gravel pack.
In some but not all wells, another way to permit hydrocarbon flow while blocking formation solid flow out of a formation is to use a screenless technique which does not require downhole mechanical equipment such as a screen or gravel pack. In a screenless completion, a mixture of fluid and particulate solids, such as proppant, is pumped into the well. This may be part of a fracturing operation during which the mixture is pumped under pressure to hydraulically fracture a formation. Upon fracture, at least a portion of the mixture is in the formation. Typically, the fluid portion returns to the well and up to the surface for disposal; the proppant, however, preferably stays in place to prop the fracture open.
To prevent flow-back of proppant as well as of loose or incompetent sand in the fractured zone with fluids produced from the zone, at least a portion of the proppant used in a screenless completion is coated with a hardenable resin composition which is caused to harden and consolidate the proppant in the zone. In one typical use, the resin composition coated proppant is deposited in the fracture after a larger quantity of uncoated proppant has been deposited therein. That is, the last portion of the proppant deposited in each fracture, referred to in the art as the xe2x80x9ctail-endxe2x80x9d portion, is coated with the hardenable resin composition. When the viscous fracturing fluid which is the carrier fluid for the proppant is broken and reverts to a thin fluid in known manner, the resin coated proppant is deposited in the fractures and the fractures close on the proppant. The partially closed fractures apply pressure on the resin coated proppant whereby the proppant particles are forced into contact with each other while the resin composition hardens. The hardening of the resin composition under pressure brings about the consolidation of the resin coated proppant particles into a hard permeable pack having sufficient compressive strength to prevent unconsolidated proppant and formation sand from flowing out of the fractures with produced fluids which are able to flow through the permeable pack.
In fracture treatments carried out in an unconsolidated formation, good consolidation of proppant is required in the perforations which extend from inside the well bore through casing and cement into the unconsolidated formation as well as in the fractured portions of the unconsolidated formation surrounding the well bore. The tail-end portion of the proppant which is deposited in the perforations and in the fractures is coated with a hardenable resin composition and caused to harden. The resulting consolidated proppant in the perforations and fractures contributes to the prevention of proppant flow-back. However, there is often little closure pressure applied to the resin coated proppant in the fractures in an unconsolidated formation, and there is no closure pressure applied to the resin coated proppant in the perforations. As a result, the consolidated permeable packs formed in the perforations and fractures may have less than sufficient compressive strength to prevent unconsolidated proppant and formation sand from flowing out of the perforations and fractures.
The above problem is complicated when the viscous carrier fluid (the fracturing fluid in the above examples) is a cross-linked gelled fluid containing a breaker which does not break for a relatively long period of time, during which the resin composition coated on the proppant hardens. At high temperatures and particularly temperatures above about 200xc2x0 F., such resin composition hardens quickly and if the viscous carrier fluid has not broken, the resin coated proppant particles are separated from each other by films of the viscous carrier fluid. As a result of the presence of the carrier fluid films, the proppant does not sufficiently consolidate and proppant flow-back occurs. Thus, when resin coated particulate solids are consolidated in subterranean zones where there is little or no closure pressure exerted on the resin coated particulate solids or when a carrier fluid used to carry resin coated particulate solids into a subterranean zone does not break before the resin hardens, or both, sufficient consolidation of the particulate solids may not take place. However, a recent invention addresses this by providing improved hardenable resin compositions which are basically comprised of a hardenable organic resin, an aminosilane resin-to-particulate solid coupling agent, a viscous carrier fluid temperature activated breaker for converting separating films of viscous carrier fluid between adjacent resin coated particulate solids to thin fluids whereby the resin coated particulate solids contact each other, and a surface active agent for causing the resin to flow to the contact points between adjacent resin coated particulate solids.
The hard permeable packs referred to above are typically made in one of two ways. One way is to mix a pre-coated particulate solid (e.g., proppant) with the viscous carrier fluid (e.g., fracturing fluid), which mixture is pumped into the well in known manner. The other technique is to form a mixture of viscous carrier fluid with liquid resin and particulate solids which become coated with the liquid resin during the action of pumping the mixture into the well. This latter technique is used for the aforementioned improved hardenable resin compositions having particular application where there is little or no formation pressure to assist the consolidation.
Until now, which type of materials (e.g., the pre-coated proppant/fracturing fluid or liquid resin/proppant/fracturing fluid materials) to use in screenless completions, and on which wells, has been somewhat of an art based on a particular job designer""s knowledge and experience. This has, unfortunately, led to job failures. Thus, there is the need for an automated, repeatably consistent process by which any oil or gas well can be evaluated as to whether it is a candidate for a screenless completion, and if it is, by which a particular screenless completion design for that candidate well can be determined.
The present invention meets the aforementioned needs by providing a novel and improved process of designing a screenless completion for one or more oil or gas wells. The present invention enables screenless completions to be more efficiently designed for oil or gas wells, and it should enable screenless completions to be used in at least some applications where prior types of screenless completion jobs in similar wells have experienced failure. The present invention also has as an object that new opportunities for screenless completions not be overlooked.
The automated process of the present invention can save on time and costs relative to prior design techniques of manually determining the feasibility of a screenless design for a specific well. The present invention provides for more consistent analysis and more consistent job design from well to well. The present invention can be used to assist completion engineers and operators in selecting a feasible and economical design for a given well.
The present invention provides a process of designing a screenless completion for an oil or gas well. One definition of this process comprises: selecting an oil or gas well having a plurality of known characteristics; inputting data about the known characteristics into a programmed computer; determining, through operation of the programmed computer, whether a screenless completion should be performed on the selected well and, if so, identifying materials to be used in the screenless completion; and in response to identifying materials to be used, indicating to a user a screenless completion design using the identified materials.
The present invention can further comprise performing the selecting, inputting, determining, identifying, and indicating steps for other oil or gas wells, wherein identifying materials includes identifying the same materials for the respective screenless completion for each well having the same value set of known characteristics for which data are input into the computer.
Identifying materials can include distinguishing, through operation of the computer, between wells for which a liquid resin, proppant and fracturing fluid are to be used and wells for which a proppant, pre-coated with resin, and fracturing fluid are to be used. For wells for which a liquid resin, proppant and fracturing fluid are to be used, preferably a liquid resin which does not substantially adversely affect the fracturing fluid and yet which coats the proppant in the fracturing fluid and enables a high compressive strength proppant pack to be obtained when placed in the well is identified.
To distinguish which wells need which materials, one or more comparisons are made in the computer with regard to input data representing one or more of a relevant temperature in the well (typically referred to as a bottom-hole temperature), angular deviation, interval length, horizontal stress contrast, fracture gradient, ability to orient perforations, formation rock properties, and whether there is or was geopressuring.
Another definition of the overall process of the present invention is as a process of designing a screenless completion for an oil or gas well, comprising: selecting an oil or gas well having a plurality of known characteristics; inputting data about the known characteristics into a computer; determining, through operation of the computer, one of three options for the selected well including (1) determining-that the selected well is not a candidate for screenless completion, (2) determining that the selected well is a candidate for screenless completion using a mixture of a carrier fluid, a hardenable resin composition, and particulate solids, and (3) determining that the selected well is a candidate for screenless completion using a mixture of a carrier fluid and particulate solids pre-coated with a hardenable resin composition before mixing with the carrier fluid; and in response to (2) or (3) above, indicating to a user one of a plurality of screenless completion designs using the respective one of the carrier fluid, hardenable resin composition and particulate solids or the carrier fluid and per-coated particulate solids.
Still another definition of the present invention is as a process of designing a screenless completion for an oil or gas well, comprising: selecting an oil or gas well having a plurality of selected known characteristics including whether there is to be new completion in the selected well or recompletion of an old zone having existing perforations, a deviation at a perforation interval, a length of the perforation interval, a fracture gradient, a degree of horizontal stress contrast, formation rock properties, whether the perforation zone is or was geopressured, and a temperature in the well; inputting data about the known characteristics into a computer; determining, through automatic operation of the computer responsive to the input data, whether a screenless completion should be performed on the selected well and, if so, identifying materials to be used in the screenless completion; and indicating to a user, through automatic operation of the computer, one of at least nine predetermined screenless completion designs, wherein the indicated one includes the identified materials and is selected by the computer in response to the input data.
A further definition of the present invention is as a process of designing a screenless completion for an oil or gas well, comprising: inputting into a computer data characterizing a perforation interval for an oil or gas well; comparing in a selected predetermined sequence in the computer input data with predetermined data correlated by characteristic of the perforation interval, including selecting the predetermined sequence in response to each compared characteristic; associating in the computer one of a plurality of predetermined screenless completion design files, stored in the computer, with the selected predetermined sequence; and displaying the associated predetermined screenless completion design file to a user such that the displayed file is used for performing the predetermined screenless completion on the oil or gas well.